(i) Field of the Invention
The present invention relates to a radio apparatus and an antenna, and in particular to a radio apparatus configured to face an external apparatus so as to perform contactless communication with the external apparatus, and to an antenna provided in the radio apparatus.
(ii) Description of the Related Art
Radio frequency identification (which will be abbreviated to RFID hereinafter) technology has been widely used for automatic ticket gates of railroads, working hour management of companies or offices, various kinds of electronic money and so on. In an RFID system, information is exchanged through radio transmission and reception between a device called a reader/writer and a data medium called a card or a tag (which is called contactless data communication). Recently, mobile phones of some types are equipped with RFID, starting from a card function and then covering a reader/writer function.
In the RFID system, an antenna included in the reader/writer and an antenna included in the card are arranged opposite and close to each other so as to communicate with each other, so that the reader/writer may write data to the card and read data from the card. A planer loop-shaped coil-like element is usually used as the antenna of the RFID system.
In a mobile phone naming the card function, e.g., a loop-shaped antenna of the RFID system is usually arranged close to either one of a front side or a back side of a casing of the mobile phone. In this case, due to a thickness of the casing, the antenna exhibits a magnetic field distribution characteristic deflected towards the side to which the antenna is arranged close. Thus, success or failure, or an error rate, in the contactless data communication is limited by an orientation of the casing to the reader/writer as well as by a separation between the casing and the reader/writer.
Related art to address such a problem is known as disclosed in, e.g., Japanese Patent Publication of Unexamined Applications (Kokai), No. 2005-26865 or No. 2005-134942. JP 2005-26865 discloses a data communication apparatus having an antenna arranged around and alone sides of a casing. JP 2005-134942 discloses a reader/writer having an antenna unit formed by a printed board contained in a main body and having multiple antennas having antenna axes in multiple directions.
The apparatus of JP 2005-26865 is configured to correct the deflection of the magnetic field distribution by positioning the antenna near a center in a thickness direction of the casing. Such a configuration, however, has a limited effect in a case of lots of mobile phones, e.g., where pivotally connected two casings are being closed to each other.
The antenna unit of the reader/writer of JP 2005-134942 has the antenna axes in a direction of a side of the main body by means of a thickness of the printed board or a layered structure of multiple printed boards. As having an effect depending on the thickness and/or the number of the printed boards, however, the antenna unit of JP 2005-134942 has difficulty in exhibiting the effect in a case where the casing is made thin.